In known optical systems, such as laser systems, an electro-optical element known as a Pockels cell is used as a polarization switching component.
A Pockels cell is a component which includes a birefringent crystal across which a variable voltage is applied in order to control polarization of light passing through the crystal. Conventional Pockels cells and their manufacture are well known in the optical arts. An exemplary transverse Pockels cell assembly is shown in FIGS. 3A and 3B at reference 300, and comprises a cylindrical, anisotropic, birefringent electro-optical crystal 308 and a cylindrical housing 306 which carries the crystal 308 as well as a pair of opposed electrodes 316. The crystal 308 has an optical axis 310 and has first and second opposed optically clear apertures 312, 314 defined by the optical axis 310 (the term “aperture” being used in its optical rather than physical sense). The electrodes 316 are electrically coupled to a control system 322 and positioned to pass an electric field transversely through the crystal 308 to control modulation of incoming light aligned with the optical axis 310.
As shown in FIG. 1, in an exemplary LiDAR system 100, polarization filters (not shown) are used to allow only one linear polarization to enter the system 100. Light L1 enters the system 100 from object space through an entrance pupil 102, which images that incoming light into the plane of an unpowered (in the optical rather than electrical sense) Pockels cell 104, which is used to electro-optically rotate the polarization axis of the light. The light then proceeds to a first relay lens 106 which collimates the image to a second relay lens 108, which focuses the image to a detector image plane 110. In this construction, the first relay lens 106 is difficult to design and manufacture. In particular, it can be seen that not only are the individual rays in each bundle diverging, but the bundles are also diverging from each other. Final image fidelity and contrast are highly sensitive to the aberration qualities of both the first and second relay lenses.